(1) Field of the Invention
The present invention relates to a pipe connecting assembly and method for joining two lengths of steel pipe in the field by a press-fit connection, the assembly and method employing a pair of steel connectors welded to or machined on opposed ends of the joined pipes.
(2) Description of the Related Art
Today, in the United States alone, there is a need to repair, replace, and generally upgrade the existing infrastructure of many communities and rural areas. Some cost estimates of the needed repairs and replacements range as high as 2 trillion dollars. Underground utility systems such as water, sewer, gas and electric or fiber optic lines make up a large and important part of this needed upgrading.
In replacing or upgrading existing underground pipeline utility systems, the traditional construction methods of open cut or trenching pipelaying may be employed. However, these methods are disruptive and costly to society, particularly in densely populated areas. Moreover, open cut or trenching construction methods of pipelaying are often prohibited in environmentally sensitive areas such as wetlands and in existing right-of-ways like highways and railroads.
Expansion, repair and replacement of underground infrastructure, particularly in urban and environmentally sensitive areas, creates the need for trenchless solutions. Trenchless methods offer many inherent advantages over traditional trenching methods and are becoming more cost effective with the ongoing development of these methods and equipment. In recent years, organizations such as the North American Society for Trenchless Technology and The American Underground Space Association have been formed. One purpose of these organizations is to increase the public awareness of trenchless methods of constructing pipelines which do not require an open cut or trench for laying pipeline and minimize the social disruption and environmental impact often associated with the traditional methods of underground utility construction. New technologies developed in other parts of the world are being introduced into the United States and Canada to meet the growing concern for the social costs and disruption of urban environments associated with traditional trenching methods of laying pipeline.
Trenchless excavation construction (T.E.C.) methods and equipment often require the use of lengths of steel pipe, because of its great compressive strength, as an encasement for underground water or sewer lines being installed. Designers of underground pipelines typically prefer using steel pipe casings because they are readily available, they are reasonably priced, and the steel pipeline casing is a forgiving material having a unique ability to bend or deflect while still offering full resistance to compression or tension loads. Steel casings are often provided around fluid transporting pipe-lines as a safety precaution to channel flow under highways and railroad tracks to prevent the possibility of soil erosion in these right-of-ways in the event of a carrier pipe leak or failure within the steel casing.
Most T.E.C. equipment and methods currently employed are designed to advance a series of connected lengths of steel casing pipe horizontally through the ground as a horizontal hole for the pipe is bored by the T.E.C. equipment. A significant problem that is most commonly encountered in T.E.C. methods of laying steel pipeline is the extent to which the forward progression of connected lengths of steel pipe pushed through the horizontal hole must be stopped for a period of time in order to weld an additional length of pipe to the series of connected pipes. The crew and equipment must stop to wait for the next length of pipeline to be attached. It is conservatively estimated that the productivity of a T.E.C. project could be increased by 25% to 50% if the welding operation time for joining two adjacent lengths of steel pipe was eliminated. In order to eliminate the need for welding adjacent lengths of pipe a steel pipe joint connection that does not require welding and which fully meets the requirements of trenchless excavation pipelaying applications is needed.
To be employed in T.E.C. methods of laying steel pipeline, a steel pipe joint connection must be designed to meet the following requirements:
a) The joint connection must be able to withstand extremely large thrust or compression forces exerted by T.E.C. equipment without deforming or leaking. The nature of the trenchless installation method requires hydraulic thrust or compression forces to be exerted by the T.E.C. equipment to advance the sequentially connected lengths of steel pipeline horizontally through the bored hole. Extended distances of the bored hole and/or compacting soil conditions require proportionately increased thrust or compression forces to be exerted on the sequential lengths of connected pipe that steel pipe can best withstand at affordable costs.
b) The joint connection between adjacent lengths of pipe must present a substantially smooth and continuous surface with the exterior surface of adjacent lengths of pipe to minimize the friction forces that act against the sequential lengths of pipe being pushed through the horizontally bored hole and to minimize the void or open space between the exterior surfaces of the lengths of pipe and the interior walls of the bored hole to avoid significant ground surface settling above the bored pipeline hole. It is an objective of trenchless excavation to displace only as much soil from the horizontally bored hole as the sequential lengths of pipe will take up when inserted through the hole to prevent ground surface settlement.
c) When utilizing sequential lengths of steel pipe as a casing pipeline containing other conductors such as water, sewer, and gas pipelines and electrical or fiber optic cables, it is necessary that the joint connection between adjacent lengths of casing pipe be substantially smooth and continuous with the interior surfaces of the casing pipe to enable the easy threading of carrier pipeline or cable through the interior of the sequentially connected casing pipeline. A smooth and continuous joint between the interior surfaces of adjacent connected pipes is also necessary when the pipeline is used as a fluid conductor to avoid producing unwanted turbulence or cavitation in the fluid flowing through the pipeline.
d) At times when an obstruction such as a bolder is encountered when boring the horizontal pipeline hole, it becomes necessary to pull the sequentially connected lengths of pipe backwards through the bored hole for necessary corrections before forward progress can be continued. Therefore, the joint connection between adjacent lengths of steel pipe must be able to withstand extremely large tension forces without being pulled apart or forming leaks.
e) The joint connection between adjacent lengths of steel pipe must be fluid tight and/or hold internal pressures which may exceed 200 pounds per square inch; if it is to function as a carrier pipe.
f) The joint connection between adjacent lengths of steel pipe must be able to transmit bending loads or moments across the connection between adjacent lengths of pipe to the extent that the adjacent lengths of pipe bend as one. T.E.C. equipment is capable of directional changes, so must be the connection.